The goal of reducing fuel consumption in vehicles has led to reductions in both engine size and vehicle weight. Attempts to maintain engine performance and load handling ability of various vehicle engines included apparatus for an increased number of available gear ratios between an engine and a vehicle drive shaft. The implementation of additional gear ratios in vehicle transmissions resulted in increased transmission costs and increased weight. Alternate approaches have suggested expansion of the number of gear ratios available in a conventional transmission with an additional gearing intermediate the main transmission and the drive shaft.
The present invention provides a shiftable planetary gear train intermediate a vehicle main transmission and a drive shaft. In German patent DE AS 2 708 524, a typical planetary gear train is described.